Placing electrical current on a moving wire is currently being done in at least the electrical discharge machine and welding industries. One common way of accomplishing this is to provide a current pickup which is generally cylindrically shaped with a bore therethrough and wherein the current pickup bore is offset from the straight line of wire travel. Thus, the taut moving wire electrode rubs against the interior surface of the bore making the necessary electrical contact for transferring current to the moving wire. An example of this type of current pickup is disclosed in U.S. Pat. No. 4,896,013.
In other current pickup devices, the current pickup is merely pushed toward the taut moving wire electrode or is placed in the normal straight line of wire travel and the tension in the wire causes the wire to rub against the current pickup thereby making the necessary electrical contact. A typical current pickup of this character is disclosed in U.S. Pat. No. 4,539,459.
Cylindrical or rod-shaped current pickups have also been used in several prior types of current conveying systems. With respect to such cylindrical/rod current pickups, the traveling wire is positioned and is caused to rub against the rod in a line perpendicular to the axis of the rod. Although a rod placed perpendicular to a moving wire is effective at conveying current, there are major drawbacks therewith. Unless the diameter of the rod is relatively large, the swept contact surface area of the rod is relatively small and the transfer of electrical current becomes inefficient while deformation of the wire is increased. In addition, the small contact surface provided by the perpendicular rod wears quickly thus requiring frequent maintenance to either adjust and provide a new contact surface or to replace the rod altogether. Further yet, increasing the perpendicular rod diameter to a sufficiently large size is undesirable because it is intrusive to other working elements of the system and prevents compact designs.
With respect to all of these types of prior current pickups, the moving wire is caused to slide or rub against an electrically charged surface, thus, transferring the electrical current therethrough to and from the moving wire. Consequently, the surface finish and shape of the current pickup in the area where the wire rubs against the current pickup is critical because electrical current must be effectively transferred while minimizing damage and wear to the wire and current pickup. Some of the most effective contact surface shapes are curvilinear, such as, for example shown in U.S. Pat. No. 4,896,013. The current pickup contact surface shapes are normally machined so as to achieve the correct curvature and surface finish. However, the machining operation is time-consuming and significantly increases the cost of the current pickups.
Accordingly, a need exists for an apparatus that conveys electrical current to and from a moving wire and which is effective at transferring the electrical current while being generally inexpensive to manufacture, efficient in terms of service life and maintenance and which concurrently provides a curvilinear-shaped contact surface.